The present application claims priority to Japanese Application(s) No(s). P2000-284292 filed Sep. 19, 2000, which application(s) is/are incorporated herein by reference to the extent permitted by law.
1. Field of the Invention
The present invention relates to a liquid crystal display device provided with a reflection electrode of a reflection diffuser panel shape formed with surface roughness and more specifically to a technique for forming an ultraviolet-reactive liquid crystal orientation film on the reflection electrode.
2. Description of the Related Art
The driving side thin film transistor (TFT) substrate of an active matrix type liquid crystal display device has, in the reflection part of a pixel, a reflection electrode of a reflection diffuser panel shape formed with surface roughness and having, in the transmission part of the pixel, a transparent electrode consisting of a transparent conductive film, thereby performing semi-transmission liquid crystal display. The driving side TFT substrate has hitherto been produced as shown in FIGS. 12A to 12J. FIGS. 12A to 12J show the processes for producing a liquid crystal display device having a TFT of a bottom gate construction in a pixel structure. A liquid crystal display device having a TFT of a top gate construction in a pixel structure is basically produced by the same production process.
As shown in FIG. 12A, a metal film is deposited on a transparent substrate 1, and then, is dry etched using the photolithographic method to form a gate G and an auxiliary capacity electrode Cs. Thereafter, a gate insulating film 2 is laminated thereon to form a polysilicon film 3.
To prevent impurities doping to a channel part during impurities doping to a source region and a drain region, a stopper 4 is formed on the polysilicon film 3 as the channel part so as to be in a self-alignment manner to the gate G, thereby performing impurities doping to the source region and the drain region.
Thereafter, the polysilicon fun 3 is separated in an island form using a photoresist process and an etching process to form a low-temperature polysilicon TFT.
An interlayer insulating film 5 is formed (FIG. 12B) To form contact holes and an opening of the transmission part of a pixel, the photoresist layer 6 is formed on the interlayer insulating film 5. A mask with a pattern opening the contact hole forming parts the transmission part of the pixel as a photo mask is used to pattern the photoresist layer 6 by the photolithographic method (FIG. 12C). Using this as an etching mask, the interlayer insulating film 5 is etched to form contact holes H1 and an opening of a transmission part T of the pixel in the interlayer insulating film 5 (FIG. 12D).
A metal film is deposited by sputtering, and then, is etched to form a source electrode S1 and a signal wiring connected through the contact hole H1 to the source S of a TFT and a drain electrode D1 connected through the contact hole H1 to the drain D of the TFT (FIG. 12E)
A rough shape as the underlayer of the surface roughness shape of a reflection electrode having reflection diffusion ability is formed as follows, using two layers made of a photoresist material. A first layer 7 forming a basic rough construction is formed using a photoresist material by the photolithographic method (FIG. 12F). There is used a photo mask opening a second contact hole H2 to be conductive with the source electrode S1 or the drain electrode D1 and the transmission part T of the pixel. A second layer 8 for improving the reflection properties is formed using a photoresist material similar to that of the first layer 7 by the photolithographic method (FIG. 12F). There is used a mask, as in the first layer 7, opening a third contact hole H3 to be conductive with the drain electrode D1 and the transmission part T of the pixel. A surface roughness shape consisting of two layers of the first layer 7 and the second layer 8 is thus formed.
A transparent conductive film 9 forming a transparent electrode of the transmission part T of the pixel is deposited using a sputtering method. The transparent conductive film 9 connected to the drain electrode D1 by the contact hole H3 (FIG. 12H). As shown in FIG. 12H, the transparent conductive film 9 is formed in the reflection part of the pixel and may be used as the underlayer of the reflection electrode.
A metal film such as Al or Ag having a high reflectivity is deposited in a reflection part R of the pixel to form a reflection electrode 10 using the photolithographic method (FIG. 12I).
A liquid crystal orientation film 30 is coated onto the entire surface of the substrate to perform an orientation process by a mechanical rubbing method (FIG. 12J). A TFT substrate having the orientation film 30 is thus completed.
A liquid crystal orientation film is also coated onto an opposing substrate formed with a color filter and an opposing transparent electrode to perform the orientation process. Thereafter, in order that both substrates hold a suitable gap, a gap material is used to superpose both substrates together by a sealing material. Liquid crystals are then implanted in the resulting substrates for sealing to provide a liquid crystal display panel.
In the prior art method for producing the driving side TFT substrate of the active matrix type semi-transmission liquid crystal display device shown in FIGS. 12A to 12J, since the orientation process is performed by the mechanical rubbing method, dust is caused during rubbing. This results in contamination of the substrate and defects due to a short circuit of the pixel electrode and the opposing electrode. Static damage due to friction is also caused. The producing yield will be lowered.
To overcome such problems, in place of the mechanical rubbing method, there is proposed an optical orientation technique in which an organic film for a liquid crystal orientation film is coated onto a substrate which is then irradiated with a polarizing ultraviolet light, so that a chemical change corresponding to the polarizing direction of the ultraviolet light is caused in the organic film to live the orientation properties and a pre-tilt angle to a liquid crystal.
As shown in FIG. 13, using the prior art optical orientation technique, a coating film 31 made of a composition for a liquid crystal orientation film is formed on the reflection electrode 10 of a reflection diffuser panel shape formed with surface roughness, and then, is radiated with a polarizing ultraviolet light L0. Incident angles xcex11 and xcex12 of the polarizing ultraviolet light L0 to the coating film 31 are not constant depending on a position on the surface roughness. A predetermined pre-tilt angle cannot be obtained. The polarizing ultraviolet light L0 passing through the coating film 31 made of a composition for a liquid crystal polarization film is reflected by the reflection electrode 10. A reflection light L1 thereof is irradiated again onto the coating film 31 (a re-irradiation phenomenon). A predetermined orientation process cannot be performed. The display quality is lowered significantly.
The liquid crystal orientation film is formed on the reflection electrode of a reflection diffuser panel shape formed with surface roughness. Similar problems are caused not only in the semi-transmission liquid crystal display device having in one pixel a reflection part formed with a reflection electrode and a transmission part made of a transparent conductive film, but also in a reflection type liquid crystal display device having a pixel electrode consisting only of a reflection electrode. They are also caused not only in the active matrix type liquid crystal display device but also in a passive type liquid crystal display device.
Accordingly, an object of the present invention is to provide a liquid crystal display device having a reflection electrode of a reflection diffuser panel shape formed with surface roughness in which when a liquid crystal orientation film is formed on the reflection electrode by an optical orientation technique without being affected by the surface roughness of the reflection electrode and a re-irradiation phenomenon from the reflection electrode, so as to realize a predetermined pre-tilt angle in the liquid crystal, thereby forming an image excellent in the display quality.
The present inventors have found the following facts. In a liquid crystal display device having a reflection electrode of a reflection diffuser panel shape formed with surface roughness, a protective film for eliminating the level difference in the surface roughness of a reflection electrode is formed on the reflection electrode by a material transparent to a visible light for absorbing an ultraviolet light, a coating film made of a composition for an ultraviolet-reactive liquid crystal orientation film is formed on the protective film, and a coating film is irradiated with a polarizing ultraviolet light to form a liquid crystal orientation film. The coating film made of a composition for a liquid crystal orientation film is formed flatly on the protective film. The incident angles of the polarizing ultraviolet light incident upon the coating film made of a composition for a liquid crystal orientation film are constant in any position of the coating film. The light passing through the coating film is reflected by the reflection electrode and is again incident upon the coating film. The intensity of the light is lowered significantly by the protective film between the coating film and the reflection electrode. The influence of the reflection light from the reflection electrode onto the orientation process of the coating film can be reduced greatly. The liquid crystal orientation film is thus formed to produce a high-quality liquid crystal display device, though the liquid crystal orientation film is formed on the reflection electrode by the optical orientation technique.
The present invention provides a method for producing a liquid crystal display device having a reflection electrode of a reflection diffuser panel shape formed with surface roughness provided on a driving substrate and an ultraviolet-reactive liquid crystal orientation film formed on the reflection electrode, comprising the following 3 steps.
(1) forming a protective film made of a material transparent to a visible light for absorbing an ultraviolet light on the reflection electrode on the driving substrate side so as to eliminate the level difference in the surface roughness of the reflection electrode;
(2) coating a composition for an ultraviolet-reactive liquid crystal orientation film onto the protective film; and
(3) forming a liquid crystal orientation film on the coating film of the composition for a liquid crystal orientation film by irradiating a polarizing ultraviolet light onto the substrate surface in the slanting direction.
In addition, the present invention provides a liquid crystal display device having a reflection electrode of a reflection diffuser panel shape formed with surface roughness provided on a driving substrate and an ultraviolet-reactive liquid crystal orientation film formed on the reflection electrode, wherein a protective film made of a material transparent to a visible light for absorbing an ultraviolet light is formed so as to eliminate the level difference in the surface roughness of the reflection electrode, and an ultraviolet-reactive liquid crystal orientation film is formed on the protective film.
According to the present invention, the liquid crystal display device is provided with the ultraviolet-reactive liquid crystal orientation film. Unlike the case that the liquid crystal orientation film is provided by the mechanical rubbing method, there are eliminated contamination and defects due to dust and static damage due to friction so as to improve the yield.
The protective film flattens the surface roughness of the reflection electrode. The protective film prevents the re-irradiation phenomenon due to the reflection light from the reflection electrode. Though the liquid crystal orientation film is formed on the reflection electrode by the optical orientation technique, a predetermined pre-tilt angle can be realized in the liquid crystal to form an image excellent in the display quality.